Mobile terminals such as a mobile phone, a Personal Digital Assistant (PDA), and the like are driven with rechargeable batteries due to their nature, and the battery of the mobile terminal is charged through supplied electric energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by foreign substances. As a result, battery charging may not be correctly performed. Further, the battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Recently, a wireless charging or a non-contact charging technology has been developed and used for electronic devices to solve the above-mentioned problem.
The wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged if the battery is put on a charging pad without connecting the mobile phone to a separate charging connector. The wireless charging technology is generally known to be used for a wireless electric toothbrush or a wireless electric shaver. The wireless charging technology can improve a waterproof function because it can be used to wirelessly charge the electronic devices. The wireless charging technology can improve the portability of the electronic devices because it does not require a wired charger. Therefore, it is expected that technologies related to the wireless charging technology will be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using resonance, and an RF/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected that the day will come when all electronic products are wirelessly charged, anytime and anywhere, without a wire in the near future on the strength of recent successful experiments configured to wirelessly transmit power to a destination spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnetic is moved in a coil, an induction current occurs. By using the induction current, a magnetic field is generated at a transmitting end, and an electric current is induced according to a change in the magnetic field so as to generate energy at a receiving end. The phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has a high energy transmission efficiency.
With respect to the resonance scheme, Prof. Soljacic of MIT announced a system in which electricity is wirelessly transferred using an electric power transmission principle of the resonance scheme based on a coupled mode theory even if a device to be charged is separated from a charging device by several meters. The wireless charging system of the MIT team employs a concept in physics that resonance is the tendency in which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork oscillates at the same frequency. The research team makes an electromagnetic wave containing electrical energy resonate instead of making sounds resonate. It is known that the resonant electrical energy does not affect surrounding machines or human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device having a resonance frequency and unused parts are reabsorbed into an electromagnetic field instead of spreading into the air.